This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 84 |
| 6 | 774 |
| 7 | 9468 |
| 8 | 146052 |
| 9 | 2764980 |
| 10 | 62759736 |
| 11 | 1678881096 |
| 12 | 52185496464 |
| 13 | 1862666455104 |
| 14 | 75581146734912 |
| 15 | 3456542059903296 |
| 16 | 176834245093202736 |
| 17 | 10053690187338014256 |
| 18 | 631507398302281340736 |
| 19 | 43596564604477924096512 |
| 20 | 3292312674449093132923488 |